Influences of severe water stress on photosynthesis, water use efficiency and proline content of almond cultivars

Abstract: Using drought tolerant almond cultivars under arid and semiarid regions such as Iran is important factor affecting production yield, especially in rainfed orchards. To evaluate responses of almond cultivars to drought stress under field condition, the experiment was carried out on six commercial cultivars namely 'Azar', 'Marcona', 'Mission', 'Nonpareil', 'Sahand', and 'Supernova'. Net photosynthesis rate (Pn) and water use efficiency (WUE) data during three stress periods indicated that Pn decreased in stress treatments, but WUE increased under stress treatments. The highest Pn occured in 'Azar' in July and August, and the highest WUE was recorded in 'Sahand' and 'Supernova'. Leaf abscission in 'Sahand' was very high and Supernova had no significant abscission. Leaf relative water content (RWC) showed a downward trend from June to August. In 'Azar', 'Nonpareil' and 'Supernova'cultivars, RWC resulted from severe stress treatment had close relationship with RWC in well-watered treatment. This result may be due to osmoregulation in leaves of stressed plants. So these cultivars could keep high water content in their leaves and tolerate severe drought stress conditions than other investigated cultivars. The highest and lowest proline accumulation was observed in the leaves of 'Marcona' and 'Sahand', respectively; both 'Marcona' and 'Sahand' were sensitive to drought stress than 'Supernova' which showed medium proline accumulation. In almond, accumulation of proline in response to longer interval between irrigation is a general trait and cannot be used as indicator for defining the tolerant trees. In general, 'Supernova' and 'Azar' showed best response under drought stress.